Next Generation Rover for Lunar Exploration Dan A. Harrison Robert Ambrose Bill Bluethmann Lucien Junkin NASA Johnson Space Center 2101 NASA Parkway Houston, Texas 77058 281-483-8315 [email protected] TABLE OF CONTENTS Within this range of surface mobility assets falls a rover that is capable of moving suited crew members and cargo. A 1. INTRODUCTION ......................................................1 team at NASA’s Johnson Space Center in Houston, Texas 2. CHARIOT CONCEPTUALIZATION ..........................2 has developed a prototype of a lunar truck, known as 3. DESIGN IMPLEMENTATION ...................................4 Chariot shown in Figure 4. The Chariot is a new 4. WHEEL MODULE...................................................4 multipurpose, reconfigurable, modular lunar surface vehicle. 5. CHARIOT FRAME...................................................5 The basic vehicle consists of a “mobility base”; that is, a 6. POWERTRAIN CONTROLLER MODULE.................7 chassis, wheel modules, electronics, and batteries. It is 7. POWER DISTRIBUTION UNIT.................................8 capable of multiple modes of operation, human direct 8. BATTERY SYSTEM ...............................................10 control from onboard, teleoperated with small time delays 9. SYSTEM SOFTWARE ............................................10 from a habitation module or lander, and supervised under 10. CREW ACCOMMODATIONS ...............................11 longer time delays from Earth. With the right attachments 11. SUMMARY ..........................................................12 and/or crew accommodations, the Chariot configuration will REFERENCES ...........................................................12 be capable of serving a large number of functions on the BIOGRAPHY .............................................................12 lunar surface. Functions will include serving as a cargo carrier, regolith mover, human transportation, and a cable layer. This lunar truck is named Chariot because of the 1. INTRODUCTION chariot-like “look” of the standing crew members driving the vehicle. A bright light appears in the starry blackness above the stark lunar landscape as a cargo lander fires its rockets for descent Lessons from Apollo to the surface. Waiting in the semi-twilight of the lunar “Dust is the number one concern in returning to the moon” south pole, a transport vehicle stands ready to assist the -Apollo 16 Astronaut John Young, July 2004 offloading and deployment of the much-needed power system and science laboratory. Meanwhile, another vehicle with a regolith moving blade attached, has just completed the excavation of the new home for the power system on the rim of Shackleton crater. As the Lander touches down several hundred meters away, the first vehicle turns and begins rolling toward it… As NASA further refines its plans for the return of humans to the lunar surface, it is becoming very clear that surface mobility will be critical to outpost buildup and exploration activities. In analyzing lunar surface scenarios, NASA’s Lunar Architecture Team (LAT) identified vehicle chassis potentially suited for lunar surface operations during their Figure 1 – Lunar Roving Vehicle Phase I study. These chassis range from small (100 kg) crew aids to very large carriers capable of moving an entire The Apollo missions 15, 16, and 17 made use of the Apollo lander. To better understand the technologies and Lunar Roving Vehicle (LRV), shown in Figure 1 above, to operations for this range of vehicles, NASA’s Exploration provide extended surface mobility in excess of the short Technology Development Program is investing in a broad walks on earlier missions. The LRVs were designed range of surface mobility projects. 1 2 primarily as crew transport vehicles with a limited amount of science payload (moon rocks) capability. Several lessons 1 2 “U.S. Government work not protected by U.S. copyright.” IEEEAC paper #1196, Final, December 5, 2007 1 were learned from the LRV operations on the moon. First, 2. CHARIOT CONCEPTUALIZATION ground speed could not exceed 10 mph in most situations. The 1/6 G environment allowed the vehicle to lose contact From the very beginning, it was decided to challenge with the surface when moderate bumps were encountered at conventional thinking about what a lunar rover should look approximately 9 mph, resulting in a momentary loss of like and how it should drive. Why is a side-by-side seating control. Second, the lunar dust behaved much like wet sand arrangement the best for suited crew? Would an inline on Earth and tended to stick to the surface (Figures 2 and 3). arrangement be better? How about four crew rather than Moon dust is extremely abrasive and dust mitigation two? With more crew members on the surface, using measures must be taken to prevent excessive wear at any multiple rovers, a four-crew capability could allow the rover place where dust can enter. The dust also has an adverse to serve as a rescue vehicle. The wheel arrangement and effect on the properties of heat radiators. Within a very number of wheels was also challenged. Aware that this short period of time, dust would cover the LRV radiators vehicle will be serving as a truck, crew hauler, regolith and the efficiency would drop precipitously. mover and more, four wheels may not be enough. With only 1/6 G and rugged terrain a six-wheeled rover would be better suited, similar to the rovers the NASA Jet Propulsion Laboratory landed on Mars. Not only do six wheels provide more traction on uneven surfaces, redundancy would be an added bonus. Figure 2. Dust-free. Figure 4. Lunar truck concept. Additionally, based on lessons learned from the LRV, it would be better for a suited crew member to have the rover’s body closer to the ground to make stepping up onto the vehicle easier. But that reduces ground clearance and Figure 3. Dust-covered after driving. would be unacceptable. The solution is a combination of passive/active suspension which is capable of lowering the Figures 2 and 3 are photos from “The Effects of Lunar Dust vehicle for easy mounting by the crew, then rising to a on Advanced Extravehicular Activity Systems: Lessons height which provides optimum clearance but would from Apollo”, James R. Gaier, NASA Glenn Research otherwise be undesirable for crew accessibility. An active Center, Ronald Creel, Science Applications International suspension provides the ability to dynamically level the Corporation. body when traversing a slope, avoiding the feeling that one is about to fall out the vehicle, that the Apollo crew noted. Additionally, the Apollo astronauts noted that with the open Redundancy in wheel modules is enhanced through active frame design, it felt as though a person could fall out of the suspension. If the steering, brake, or drive of a wheel vehicle while traversing a steep slope. A review of Apollo module fails, that wheel can be lifted off the surface and the Lunar Rover operations indicated room for improvement in vehicle goes home on five wheels. This is not possible with ride, suit interfaces, and reliability. Apollo mission reports a four-wheeled configuration. indicate the vehicle performed well during operations, but driving on cross slopes was described as feeling “very Last, much thought was given as to how the vehicle should uncomfortable” by the operators. Suit interfaces for the be steered. The concept which won out was “crab steering.” Apollo LRV posed challenges for astronauts attempting to Crab steering means each of the six wheels can rotate 360 sit in the LRV seat. The chief problem was the rigidity of degrees, giving the vehicle the ability to move in any the suit torso and the difficulty in bending at the waist, as direction or rotate at any point. This makes maneuvering in required for sitting. Lastly, rovers designed for the return to tight places possible where a conventionally steered vehicle the lunar surface will be required to have a much greater could not operate. This would be a more mechanically lifespan, a longer range, and be rechargeable. complex challenge. Whereas, the LRV had a motor on each wheel hub, a crab steering design requires that the motors be 2 located away from the wheels, and that the wheel be driven – Continuous rotation by a driveshaft for full 360 degree rotation. Here, the huge – 380 ft-lb gain in flexibility is deemed of greater value than the added – 145 deg/s complexity of crab steering. • Drive Chariot Requirements/Specifications – Six dual wheels – 20 km/hr top speed The LAT, Phase I, defined a lunar surface vehicle – Two-speed transmission designated as “Chassis B” that would serve as a primary – 20 HP (full vehicle) mobility base, meant for use in systems such as – 4000 ft-lb max torque (full vehicle) unpressurized rovers and in-situ resource utilization (ISRU) – Open differential, with drop in limited slip transport, with a planned life of 5 years. The vehicle was differential not sized for use in permanently shadowed crater areas. – Capable of climbing 15 degrees (slope in 1g) – Two wheels per module The vehicle should have multiple control modes, human – Neutral and brake direct onboard driving, be teleoperated from a habitat module and teleoperation from Earth. The power systems • Wheels should be sized to provide extended mobility and limited – Modular hub power to payloads. It should have navigation sensors and – Fenders basic communications infrastructure with up to 2Mb/sec – Pneumatic options transfer rates to locations on the moon or directly to Earth,